Add a stub for add()

src/ArduinoJson/Array/JsonArray.hpp

@@ -158,6 +158,12 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
     return data_ ? data_->size(resources_) : 0;
   }
 
+  // DEPRECATED: use add<JsonVariant>() instead
+  ARDUINOJSON_DEPRECATED("use add<JsonVariant>() instead")
+  JsonVariant add() const {
+    return add<JsonVariant>();
+  }
+
   // DEPRECATED: always returns zero
   ARDUINOJSON_DEPRECATED("always returns zero")
   size_t memoryUsage() const {

src/ArduinoJson/Document/JsonDocument.hpp

@@ -291,6 +291,12 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
     swap_(a.data_, b.data_);
   }
 
+  // DEPRECATED: use add<JsonVariant>() instead
+  ARDUINOJSON_DEPRECATED("use add<JsonVariant>() instead")
+  JsonVariant add() {
+    return add<JsonVariant>();
+  }
+
   // DEPRECATED: always returns zero
   ARDUINOJSON_DEPRECATED("always returns zero")
   size_t memoryUsage() const {

src/ArduinoJson/Variant/VariantRefBase.hpp

@@ -221,6 +221,10 @@ class VariantRefBase : public VariantTag {
                                   MemberProxy<TDerived, TChar*>>::type
   operator[](TChar* key) const;
 
+  // DEPRECATED: use add<JsonVariant>() instead
+  ARDUINOJSON_DEPRECATED("use add<JsonVariant>() instead")
+  JsonVariant add() const;
+
   // DEPRECATED: always returns zero
   ARDUINOJSON_DEPRECATED("always returns zero")
   size_t memoryUsage() const {

src/ArduinoJson/Variant/VariantRefBaseImpl.hpp

@@ -10,6 +10,11 @@
 
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
+template <typename TDerived>
+inline JsonVariant VariantRefBase<TDerived>::add() const {
+  return add<JsonVariant>();
+}
+
 template <typename TDerived>
 inline void convertToJson(const VariantRefBase<TDerived>& src,
                           JsonVariant dst) {